The present invention relates to a document to be protected against forgery, comprising a security feature in the form of a perforation pattern.
Such a document is known from the international patent application PCT/NL95/00119.
In this prior art document the perforation pattern takes the form of a character or a number of characters. This perforation pattern is herein applied in the form of round, rectangular, or character-like perforations. These perforation patterns are therefore always representations of a black and white image without intensity differentiation.
Although making these perforations already raises a considerable barrier for potential forgers, there exists a need for a security feature which is even more difficult to forge.
This object is achieved in that the perforation pattern extends over a surface of the document and represents an image comprising brightness tones.
The perforation pattern is herein formed such that, for instance when the thus treated document is held up to the light or placed on a light box, an image becomes visible at the location of the perforation pattern.
It will be apparent that arrangement of such an image representing brightness tones requires extremely advanced technologies. Such technologies are not easily accessible to potential forgers, so that documents thus provided with such a perforation pattern are very difficult to forge.
The perforation pattern is preferably applied by means of laser light.
This measure has the advantage that at the position of the perforation the material, for instance paper, plastic or textile is completely removed, so that when for instance the fingertips brush over the document no elevation or channel or burr can be felt at all.
If for instance a perforation pattern were to be applied by forgers by means of for instance conically formed needles, cup-shaped edges or burrs are always created which are easily discernible with the fingertips. This therefore provides a good means of identifying possible forgeries.
According to yet another preferred embodiment, the perforation pattern is a representation of an image arranged on the document by means of a different technique.
Owing to the possibility of visually comparing the image and the perforation, thus without the deployment of complicated assist means being required, a less than perfect forgery of just one of the two becomes immediately recognizable. A high degree of security against fraud is thus obtained.
This measure requires that, in order to make such a document, there must be present means for making the perforation pattern and means for making the associated image with a different technique, respectively means for recording this image and putting it into digital form to enable control of the means necessary for making a perforation pattern.
According to yet another preferred embodiment, the image arranged by means of a different technique is specific to the document. This provides the option of personalizing the document. It will be apparent that this results in an even higher level of security.
An important application of the present invention lies in the fact that the document is a passport and that the image is a passport photograph.
Other preferred embodiments are stated in the remaining sub-claims. It is pointed out here that the invention also relates to a method for applying a security feature in the form of a perforation pattern in a document, wherein the perforation pattern is applied by a laser device which is adapted to successively apply a perforation pattern in the document, wherein the size of the perforation holes or the density of the perforation holes is controlled by means of an electronic representation of the image.
The present invention also relates to a device for performing such a method.